1. Technical Field of the Invention
The present invention relates to a technique for recording or reproducing information to an optical disk used as a storage medium.
2. Description of the Related Art
In recent years, variety of optical disk drives are developed in addition to a CD format for only reproduction in the field of the optical disk drive, for example, the disk drives for write-once type CD-R, CD-RW which allows repeated recording and reproducing operations, DVD-ROM which realizes high density reproducing operation of about seven times the density of CD, write-once type DVD-R and moreover DVD-RAM which allows repeated recording and reproducing operations, or the like. In these optical disk drives, information is recorded and reproduced by irradiating the information recording surface of an optical disk with an optical spot of laser beam and the positioning of optical spot for each track in the radius direction of optical disk is conducted through the control for position of objective lens with an actuator (hereinafter, referred to as tracking control) and the control for feed position of pickup on which the actuator is mounted (hereinafter, referred to as feed control). As the track width is narrowed with transfer of disk to DVD from CD, higher accuracy is required as the positioning accuracy between the optical axis of objective lens of actuator and the optical axis of laser mounted on the pickup. In the case of CD, such accuracy required is ±0.6 mm, while in the case of DVD-ROM, the required accuracy is ±0.3 mm.
In the case of DVD-RAM for recording information by generating a phase change on the disk surface utilizing generation of heat with a laser beam spot in order to conduct information recording on the optical disk, amount of optical beam must be acquired under the condition that the laser beam spot conforming to the Gaussian distribution is positioned with severe accuracy and the positioning accuracy between the optical axis of the objective lens of the actuator and the optical axis of the laser of optical pickup must be controlled within the range of ±0.1 mm. In view of realizing such positioning accuracy, as an optical pickup feed mechanism, the mechanism in which a screw is rotated with a stepping motor which can freely select by itself the rotating steps from a minute step to a large step is introduced and thereby the positioning control of the optical pickup can be realized.
The characteristics required for the optical pickup utilizing a stepping motor are that the optical pickup can be moved quickly without any problem at the time of random access and positioning can be realized accurately after the movement. In the case of DVD-ROM, the characteristics that the random access time is almost 90 ms and positioning accuracy between the optical axis of the objective lens of actuator and the optical axis of laser of optical pickup is ±0.3 mm have been realized. In the case of DVD-RAM, the characteristics that the positioning accuracy corresponding to ±0.1 mm is obtained, rotation step of the stepping motor is increased and quick movement of the optical pickup is realized by increasing a drive current have been attained by dividing the pitch of the screw mounted to the stepping motor.
When a stepping motor is used to move the optical pickup in an optical disk drive, a value attained by adding a sufficient margin load to the maximum load value which is assumed when the optical pickup is moved can be estimated as the total load to be driven with the motor and a drive torque of such stepping motor has been set as a value corresponding to such value. A slide resistance generated against a shaft to support the optical pickup and a slide resistance generated between the stepping motor and components to be engaged with the optical pickup can be considered as a moving load of the optical pickup observed from the stepping motor side and these slide resistances are changed depending on the gravity working on the optical pickup, aging deterioration of each component and ambient environment such as peripheral temperature and humidity.
With recent wide spreading of a notebook-size personal computer, an optical disk drive to be loaded into such small size personal computer is requested to realize further reduction in thickness and power consumption, while a stepping motor to move the optical pickup is also requested to realize also resulting reduction in thickness and power consumption based on the precondition that variation of the optical pickup moving load can be surely covered. The technique regarding reduction of power consumption of the stepping motor is described, for example, in the Japanese Unexamined Patent Publication No. 306701/1999, but this technique also includes a problem that a detecting means or the like provides possibility for increase of manufacturing cost of the drive. As the technique for controlling a current of a stepping motor depending on variation of the moving load of the optical pickup in which the influence by change of temperature environment and aging deterioration of components is considered, this publication describes the technique that a synchronism of the stepping motor is detected by comparing the number of pulses to drive the stepping motor with the number of tracks crossed on the optical disk and a drive current of the stepping motor is compensated for recovery from a synchronism.
Considering the background explained above, an object of the present invention is that power consumption can be lowered under the construction that increase of manufacturing cost of an optical disk drive is controlled and the predetermined movement of an optical pickup can be assured by covering variation of load such as a slide resistance of the optical pickup with change of a drive torque.